Image processing apparatus and image processing method

ABSTRACT

The third image signal is generated by multiplying the second image signal constituted by low-frequency components by K. If the fourth image signal obtained by adding the third image signal to the first image signal constituted by high-frequency components falls within a predetermined range, the third image signal is output, whereas if the fourth image signal includes a portion exceeding the range, an image signal obtained by correcting the third image signal is output. A composition signal of the output image signal and the first image signal is generated. The fifth image signal is generated by multiplying the third image signal by a correction amount γ of the third image signal. As a sub-frame of interest, either the composition signal or the fifth image signal is output.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a moving image processing technique.

2. Description of the Related Art

Liquid-crystal display devices have recently been used as TV receiversand display devices for PCs. Such liquid-crystal display devices can beformed into flat panel structures to save space and power, and hence arewidely used. However, these liquid-crystal display devices have lowresponse speed with respect to moving images. As a method of drivingliquid-crystal display devices to improve response speed, there has beenproposed a method of performing overdriving in accordance with theresult of comparison between image data to be displayed next andprevious image data (patent reference 1 (Japanese Patent Laid-Open No.11-126050)).

In addition, as a method of improving motion blurring due to the displaycharacteristics of a liquid-crystal display device, there has beenproposed a driving method that inserts a black frame or intermediateimage by doubling the frame frequency of an input image signal (patentreference 2 (Japanese Patent Laid-Open No. 2002-351382)).

If, however, the amount of change in high-frequency component is large,an obtained value may exceed the display range. This leads to failuressuch as display deterioration and the display of unnecessary videocomponents. If, for example, the LPF constant is changed to overcomesuch failures, the motion blurring improvement effect decreases(deteriorates).

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the aboveproblems, and provides a technique of enabling display fully using thedynamic range of display tones without collapse of high-frequencycomponents, and avoiding the display of unnecessary pseudo-components.

According to one aspect of the present invention, there is provided animage processing apparatus which processes and outputs an image signalinput for each frame, comprising: a division unit which divides oneframe into a plurality of sub-frames; an acquisition unit which acquiresa first image signal constituted by high-frequency components and asecond image signal constituted by low-frequency components from animage signal of a sub-frame of interest; a unit which generates a thirdimage signal by multiplying the second image signal by a constant valueK satisfying 0<K<1; a process unit which outputs the third image signalwhen a fourth image signal obtained by adding the first image signal andthe third image signal falls within a predetermined range and outputs,when the fourth image signal includes a portion exceeding the range, animage signal obtained by correcting the third image signal so as thatthe portion does not exceed the range; a unit which generates acomposition signal of the image signal output from the process unit andthe first image signal; a unit which generates a fifth image signal bymultiplying the third image signal by a constant value (2−γ) when γrepresents a correction amount for the third image signal from theprocess unit; and an output unit which outputs one of the compositionsignal and the fifth image signal as the sub-frame of interest.

According to another aspect of the present invention, there is providedan image processing method performed by an image processing apparatuswhich processes and outputs an image signal input for each frame,comprising the steps of: dividing one frame into a plurality ofsub-frames; acquiring a first image signal constituted by high-frequencycomponents and a second image signal constituted by low-frequencycomponents from an image signal of a sub-frame of interest; generating athird image signal by multiplying the second image signal by a constantvalue K satisfying 0<K<1; outputting the third image signal when afourth image signal obtained by adding the first image signal and thethird image signal falls within a predetermined range and outputting,when the fourth image signal includes a portion exceeding the range, animage signal obtained by correcting the third image signal so as thatthe portion does not exceed the range; generating a composition signalof the image signal output in the step of processing and the first imagesignal; generating a fifth image signal by multiplying the third imagesignal by a constant value (2−γ) when γ represents a correction amountfor the third image signal in the step of processing; and outputting oneof the composition signal and the fifth image signal as the sub-frame ofinterest.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing processing which a sub-frame imagegeneration unit 103 performs for a sub-frame of interest;

FIG. 2 is a view showing an example of the arrangement of a projectiontype display device, more specifically, an engine unit D1, to which animage processing apparatus according to the first embodiment of thepresent invention is applied;

FIG. 3 is a block diagram showing an example of the hardware arrangementof a projection type display device 200 to which the image processingapparatus according to first embodiment of the present invention isapplied;

FIG. 4 is a block diagram showing an example of the functionalarrangement of the sub-frame image generation unit 103;

FIG. 5A is a graph showing the relationship between the low-frequencycomponents and the high-frequency components separated by an LPF 402;

FIG. 5B is a graph showing the relationship between low-frequencycomponents and outputs from an adder 408;

FIG. 5C is a graph for explaining the processing of operatinglow-frequency components to remove portions 680 and 690 which exceed a Drange;

FIG. 5D is a graph showing the results obtained by adding high-frequencycomponents to processed low-frequency components;

FIG. 6 is a block diagram showing an example of the functionalarrangement of a sub-frame image generation unit 103 according to thesecond embodiment of the present invention; and

FIG. 7 is a block diagram showing an example of the functionalarrangement of a sub-frame image generation unit 103 according to thethird embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention will be described below withreference to the accompanying drawings. Note that each embodimentdescribed below is a specific example of the present invention, and is aconcrete embodiment of the arrangement described in the appended claims.

First Embodiment

FIG. 2 is a view showing an example of the arrangement of a projectiontype display device, more specifically, an engine unit D1, to which animage processing apparatus according to this embodiment is applied.Liquid-crystal panels 2R, 2G, and 2B as light modulation devicesrespectively corresponding to R, G, and B are arranged at positionsfacing a cross prism 7. This embodiment uses TN liquid-crystal panels,as the liquid-crystal panels 2R, 2G, and 2B, which are driven by usingTFTs. Polarizing plates 8 are arranged on the two sides of each of theliquid-crystal panels 2R, 2G, and 2B. A projection lens 9 and a screen(a member on which projection is performed) 6 are arranged on the lightexit side of the cross prism 7.

A parabolic reflector 10 surrounds a lamp (light source) 1 and isconfigured to convert exit light L1 from the lamp 1 into a parallellight beam L2. The reflector 10 need not be parabolic, and may be, forexample, elliptic. In this case, the reflector 10 converts the exitlight L1 from the lamp 1 into a condensed light beam.

As the lamp 1, a metal halide lamp, a xenon lamp, or the like can beused. Fly-eye integrators 40 and 41 are arranged on the optical path oflight emitted from the lamp 1 so as to have a conjugate relationshipwith the liquid-crystal panels 2R, 2G, and 2B, thereby improving thenonuniformity of the light source.

A relay lens 11 and a mirror 12 are sequentially arranged on the lightexit side of the fly-eye integrators 40 and 41. Two dichroic mirrors 13and 14 are arranged on the subsequent stage to cause emitted light fromthe lamp 1 to branch into three light beams. A relay lens 15 and mirrors16, 17, and 18 are arranged to guide the respective light beamsbranching from the emitted light to the liquid-crystal panels 2R, 2G,and 2B. Reference numeral 19 denotes a field lens. As shown in FIG. 3, avideo signal processing apparatus 3 having the arrangement exemplifiedby FIG. 3 is connected to the liquid-crystal panels 2R, 2G, and 2B.

FIG. 3 is a block diagram showing an example of the hardware arrangementof a projection type display device 200 to which an image processingapparatus according to this embodiment is applied. In the video signalprocessing apparatus 3, a switch 30 selects one of the video signalinput from a PC (Personal Computer) via a terminal 50 and the AV signalinput from a terminal 51, and outputs the selected signal to an A/Dconverter 31 on the subsequent stage. The AV signal includes signalsconforming to various types of standards such as NTSC and a video signalof a general TV broadcast program. This AV signal also includes thevideo signals obtained from a recording device (a video deck, DVDrecorder, or HDD recorder) that records video signals on a medium and aplayback device (a DVD player, LD player, or the like) which plays backa video signal recorded on a medium.

A signal processing circuit 52 performs signal processing, such as AVsignal decoding, noise reduction processing, band-limit filtering, andsignal level adjustment, for the AV signal input from the terminal 51.The A/D converter 31 converts an analog image signal, which is the videosignal (image signal) output from the switch 30, into a digital imagesignal. The A/D converter 31 sends this converted digital image signalto a DSP (Digital Signal Processor) 32 on the subsequent stage.

The DSP 32 executes predetermined signal processing for the digitalimage signal received from the A/D converter 31, and outputs theexecution result to a frame rate conversion unit 101. This predeterminedsignal processing includes image processing such as contrast adjustment,bright adjustment, color conversion, and resolution conversion.

The frame rate conversion unit 101 converts the frame rate of thedigital image signal input from the DSP 32. A memory 33 stores the imagedata of the current frame and the image data of the next frame.Obviously, the memory 33 may store other necessary information, asneeded.

A TG (Timing Generation circuit) 34 outputs a timing signal that definesan operation timing for each unit constituting the projection typedisplay device 200. A sub-frame image generation unit 103 processes thedigital image signal output from the frame rate conversion unit 101 toimprove a moving image characteristic such as moving image blurring. Apolarity reversal unit 106 reverses the polarity of the digital imagesignal processed by the sub-frame image generation unit 103. A D/Aconverter 35 converts the digital image signal, whose polarity isreversed by the polarity reversal unit 106, into an analog image signal,and outputs the converted analog image signal to a panel driver 36.

The panel driver 36 sends the R, G, and B component signals of thisanalog image signal to the liquid-crystal panels 2R, 2G, and 2B,respectively. The panel driver 36 supplies power to each of theliquid-crystal panels 2R, 2G, and 2B. Obviously, it is also effective toprovide the projection type display device 200 with digital signal inputterminals such as LVDS and TMDS and a D4 terminal for digital TVs inaddition to the above arrangement. A ballast 57 is a lamp power supplyconnected to the lamp 1. Reference numeral 58 denotes a system powersupply; and 60, an AC inlet.

The user operates a remote controller 61 to issue various instructionsto the projection type display device 200. A control panel 62 receivesthe instruction signal sent from the remote controller 61, decodes it,and notifies a CPU 63 of the resultant information. A brightnessadjustment SW (switch) detection unit 109 detects the operation of abrightness adjustment SW (switch) 204.

The CPU 63 controls the overall apparatus by using computer programs anddata stored in a ROM 64 and a RAM 65. The ROM 64 stores set data in thisapparatus and information described as known information. When some ofthe above units constituting the video signal processing apparatus 3 areto be implemented by computer programs, the ROM 64 stores them, and theCPU 63 executes them.

The RAM 65 has an area for temporarily storing data externally receivedvia a USB I/F 107 and a work area to be used by the CPU 63. Referencenumeral 121 denotes a terminal for receiving various kinds of externalinformation (USB outputs). The USB I/F 107 functions as an I/F forreceiving the information input via the terminal 121.

The operation of the frame rate conversion unit 101 will be describednext in detail.

The frame rate conversion unit 101 divides the image signal of one frameinto the image signals of N (N≧2: N is an integer) sub-frames. This alsoincreases the frame rate by N times. This embodiment will exemplify acase in which N is two. The embodiment will exemplify, for example, acase in which an input image signal having a vertical frequency of 60 Hzis converted into a signal having a double-vertical frequency (120 Hz)frame rate. In this case, the memory 33 stores the input image of atleast one frame. Changing the read speed of input image data from thememory 33 can convert the input image signal into an image signal havinga different frame rate.

The operation of the sub-frame image generation unit 103 will bedescribed in more detail next. FIG. 4 is a block diagram showing anexample of the functional arrangement of the sub-frame image generationunit 103. The sub-frame image generation unit 103 sequentially receivesthe respective sub-frames constituting one frame, processes them, andoutputs the resultant information.

A subtractor 407 and an LPF (Low-Pass Filter) 402 receive the imagesignal of a sub-frame of interest output from the frame rate conversionunit 101 via a terminal 401. In this case, this image signal isconstituted by high-frequency components H and low-frequency componentsL. Referring to FIG. 4, the image signal input via the terminal 401 isrepresented by H+L.

The LPF 402 outputs an image signal L (second image signal) constitutedby low-frequency components by cutting the high-frequency components ofthe input image signal H+L. The subtractor 407 and a coefficient unit403 receive the image signal L.

The subtractor 407 outputs an image signal H (first image signal)constituted by the high-frequency components by subtracting thelow-frequency components, i.e., the image signal L, from the imagesignal H+L input via the terminal 401.

The coefficient unit 403 generates and outputs an image signal KL (thirdimage signal) by multiplying the image signal L by a coefficient K (aconstant value K satisfying 0<K<1). In this embodiment, since the numberof sub-fields is two, ½, which is the reciprocal of two, is used as K.Therefore, the third image signal is expressed as an image signal L/2.This is because, in this embodiment, low-frequency components aredisplayed ½ by ½ with respect to two sub-frames.

An adder 408 generates an image signal H+L/2 by adding the image signalL/2 output from the coefficient unit 403 to the image signal H outputfrom the subtractor 407, and then outputs the signal H+L/2 as the fourthimage signal. However, if the image signal H constituted byhigh-frequency components is added to the image signal L/2 constitutedby low-frequency components, a portion exceeding a predetermined displayrange (D range) may occur. This portion cannot be displayed, and hencethe high-frequency components are displayed while being caused tocollapse and distorted, resulting in great deterioration of imagequality.

This embodiment therefore processes the image signal L/2 so as to removethe portion exceeding the display range (in general, the range of videosignal levels (D range) which a device to which an image signal isoutput can express).

Upon receiving the image signal H+L/2 from the adder 408, a displayrange over detection unit 409 checks whether a portion exceeding the Drange is included (exists) in the image signal H+L/2. If such a portionexists, the display range over detection unit 409 notifies a tonecontrol unit 410 on the subsequent stage of the correspondinginformation.

Upon receiving the image signal L/2 from the coefficient unit 403, thetone control unit 410 controls the tone of the image signal L/2 bymultiplying the image signal L/2 by a coefficient γ (correction amount)so as to remove the portion exceeding the D range, and outputs an imagesignal L/2 xγ after control. Upon determining that there is no portionexceeding the D range (the signal falls within the display range), thedisplay range over detection unit 409 notifies the tone control unit 410of the corresponding information. The tone control unit 410 thereforeoutputs the image signal L/2 received from the coefficient unit 403without any change (in this case, γ=1).

Upon receiving the image signal L/2 from the coefficient unit 403, atone control unit 404 controls the tone of the image signal L/2 bymultiplying the image signal L/2 by a coefficient 2−γ, and outputs animage signal L/2 x(2−γ) after control as the fifth image signal.

An adder 411 generates and outputs an image signal H+L/2 xγ as acomposition signal by adding the image signal H output from thesubtractor 407 to the image signal output from the tone control unit 410(image signal L/2 xγor the image signal L/2).

A selector 405 receives the image signal H+L/2 xγ from the adder 411 andthe image signal L/2 x(2−γ) from the tone control unit 404. The selector405 alternately outputs these signals for each sub-frame. Assume that aframe of interest has the first sub-frame, the second sub-frame, thethird sub-frame, . . . . In this case, when the terminal 401 receivesthe image signal of the first sub-frame, the selector 405 selects theimage signal H+L/2 xγ as an image signal for playing back the firstsub-frame, and outputs it. Subsequently, when the terminal 401 receivesthe image signal of the second sub-frame, the selector 405 selects theimage signal L/2 x(2−γ) as an image signal for playing back the secondsub-frame, and outputs it. When the terminal 401 receives the imagesignal of the third sub-frame, the selector 405 selects the image signalH+L/2 xγ as an image signal for playing back the third sub-frame, andoutputs it. In this manner, the selector 405 alternately selects thesesignals on a sub-frame basis, and outputs them. An output from theselector 405 is sent to the polarity reversal unit 106 on the subsequentstage via a terminal 406.

The operation of the display range over detection unit 409 and tonecontrol unit 410 will be described in more detail next with reference toFIGS. 5A to 5D. Referring to FIGS. 5A to 5D, the abscissa represents thelow-frequency component level (L) of a pixel of interest; and theordinate, the result obtained by adding the low-frequency component Land the high-frequency component H (i.e., an output from the adder 411or the adder 408). The amount by which a high-frequency component isadded to a low-frequency component of an image differs for each pixel.

FIG. 5A is a graph showing the relationship between the low-frequencycomponents and the high-frequency components separated by the LPF 402.Referring to FIG. 5A, reference numeral 501 denotes the levels oflow-frequency components; and 502, 503, and 504, high-frequencycomponents superimposed on low-frequency components. In this case, theamount by which a high-frequency component is superimposed on alow-frequency component differs for each pixel in accordance with adisplay image.

FIG. 5B is a graph showing the relationship between low-frequencycomponents and outputs from the adder 408. As shown in FIG. 5B, when His added to L/2, portions 680 and 690 (indicated by the hatching)exceeding the display range (D range) are generated. As described above,since these portions cannot be displayed, the high-frequency componentscollapse, resulting in a distorted image. That is, the image qualitygreatly deteriorates. This embodiment has an object to remove theportions 680 and 690.

FIG. 5C is a graph for explaining the processing of operatinglow-frequency components to remove the portions 680 and 690 exceedingthe D range. This processing improves the deterioration of imagequality. More specifically, a low-frequency component on which ahigh-frequency component including the portion 680 is superimposed isbiased (multiplied by γ) by the amount denoted by reference numeral 702.This raises the tone conversion characteristic 601 of the low-frequencycomponent, on which the high-frequency component including the portion680 is superimposed, by the amount denoted by reference numeral 702(=amount denoted by reference numeral 602). Likewise, a low-frequencycomponent on which a high-frequency component including the portion 690is superimposed is biased (multiplied by γ) by the amount denoted byreference numeral 703. This raises the tone conversion characteristic601 of the low-frequency component, on which the high-frequencycomponent including the portion 690 is superimposed, by the amountdenoted by reference numeral 703 (=amount denoted by reference numeral603). With these processes, a tone conversion characteristic 701 isobtained. This removes the portions 680 and 690.

FIG. 5D is a graph showing the results obtained by adding high-frequencycomponents to low-frequency components processed in the above manner. Asdenoted by reference numerals 802 and 803, portions exceeding the Drange are removed. This can make the high-frequency components fallwithin the D range without collapse and distortion. In this case, it ispossible to perform filter processing so as to make the tone conversioncharacteristic have smooth changes between tones. In addition, thearrangement for tone conversion may include a LUT (LookUp Table) using amemory or a circuit for performing function calculation. Alternatively,adjusting the timing of computation by using a delay circuit and thelike can process an image exceeding the display range in real time.

If, for example, a computation result is reflected in an image with adelay of one frame, no problem arises in the case of still images. Inthe case of moving images, however, the display position of a pixelexceeding the display range differs from that of an image reflecting thecomputation result.

According to the above description, this embodiment allows the displaydevice to perform display fully using the dynamic range of display toneswithout collapse of high-frequency components even in a case in which amoving image characteristic such as moving image blurring is improved.In addition, it is possible to avoid the display of unnecessary pseudocomponents and improve the moving image characteristics without anydeterioration of image quality.

FIG. 1 is a flowchart for processing which the sub-frame imagegeneration unit 103 performs for a sub-frame of interest. In practice,therefore, the sub-frame image generation unit 103 performs processingfor the image signal of each sub-frame in accordance with the flowchartshown in FIG. 1.

First of all, in step S101, the LPF 402 outputs the image signal Lconstituted by low-frequency components by cutting high-frequencycomponents of the input image signal H+L. The subtractor 407 and thecoefficient unit 403 receive the image signal L.

In step S102, the subtractor 407 outputs the image signal H constitutedby high-frequency components by subtracting the low-frequencycomponents, i.e., the image signal L, from the image signal H+L inputvia the terminal 401. In step S103, the coefficient unit 403 generatesand outputs the image signal L/2 by multiplying the image signal L by acoefficient of ½ as a constant value.

In step S104, the adder 408 generates and outputs the image signal H+L/2by adding the image signal L/2 output from the coefficient unit 403 andthe image signal H output from the subtractor 407.

In step S105, upon receiving the image signal H+L/2 from the adder 408,the display range over detection unit 409 checks whether the imagesignal H+L/2 includes any portion exceeding the D range. If the signalincludes a portion exceeding the D range, the process advances to stepS107. If the signal includes no portion exceeding the D range, theprocess advances to step S106.

In step S106, the tone control units 410 and 404 set γ to 1. In stepS107, upon receiving the image signal L/2 from the coefficient unit 403,the tone control unit 410 generates and outputs the image signal L/2 xγby multiplying the image signal L/2 by the coefficient γ. In addition,upon receiving the image signal L/2 from the coefficient unit 403, thetone control unit 404 generates and outputs the image signal L/2 x(2−γ)by multiplying the image signal L/2 by the coefficient 2−γ.

In step S108, the adder 411 generates and outputs the image signal H+L/2xγ by adding the image signal H output from the subtractor 407 and theimage signal L/2 xγ output from the tone control unit 410.

In step S109, the selector 405 outputs either the image signal H+L/2 xγfrom the adder 411 or the image signal L/2 x(2−γ) from the tone controlunit 404.

This embodiment has exemplified the case in which when a frame isdivided into N sub-frames, a high-frequency (H) component image isdisplayed in one of the N sub-frames, and a low-frequency (L) componentimage is divided and displayed 1/K by 1/K in each of the N sub-frames.However, the present invention is not limited to this. It is possible todisplay an H component at Kx magnification and an L component at 1×magnification as long as the ratio between the H component and the Lcomponent satisfies a desired condition (H:L=K:1).

Second Embodiment

This embodiment divides the display area of an image into a plurality ofpartial areas and performs the processing described in the firstembodiment for each partial area. FIG. 6 is a block diagram showing anexample of the functional arrangement of a sub-frame image generationunit 103 according to this embodiment. The same reference numerals as inFIG. 4 denote the same parts in FIG. 6, and a description of them willbe omitted.

A display area discrimination unit 901 determines an area within thedisplay screen by counting HD and VD sync signals and pixel clocks CLK.An area correction value storage unit 902 stores the D range over amount(the amount by which the D range is exceeded) detected by a displayrange over detection unit 409 for each area. An inter-area interpolationcomputation unit 903 performs correction by using a tone conversioncharacteristic corresponding to an area including the display positionof a pixel of interest.

When performing interpolation, the inter-area interpolation computationunit 903 acquires correction values for four neighboring areas relativeto the low-frequency component value of a pixel of interest,interpolates the values in accordance with the display positions withinthe areas, and uses the resultant values. It is possible to use, as aninterpolation method, linear interpolation, cubic interpolation, thespline method, or the like.

This embodiment can perform tone control for each area and optimallycontrol black and white levels for each area. This allows the effectiveuse of the display range (dynamic range) within the display screen. Itis therefore possible to display a well-contrasted image.

Third Embodiment

In this embodiment, a display range over amount adjustment unit 1001 canadjust the D range over amount in accordance with a display image byadjusting the D range over amount detected by a display range overdetection unit 409. This can implement image quality control accordingto user's preference.

FIG. 7 is a block diagram showing an example of the functionalarrangement of a sub-frame image generation unit 103 according to thisembodiment. The same reference numerals as in FIG. 4 denote the sameparts in FIG. 7, and a description of them will be omitted. The displayrange over amount adjustment unit 1001 obtains a D range over amount Cby performing the processing based on the following equation for a Drange over amount A detected by the display range over detection unit409.

D range over amount C=D range over amount A−adjustment amount B

The display range over amount adjustment unit 1001 sends the D rangeover amount C again to the display range over detection unit 409. Thedisplay range over detection unit 409 therefore checks whether the Drange over amount C exceeds the D range. This makes it possible for thedetection range of D range over amounts to have a certain width.Obviously, the subsequent processing will use the D range over amount C.

For example, the tones of an image actively caused to collapse dependingon the image. In this case, it is possible to trade off portionsexceeding the display range to some extent. This is because it is notalways necessary to display all the tones. In this case, a DSP 32computes and determines the adjustment amount B based on the luminanceinformation of an image (the distribution, average luminance, maximumluminance, and minimum luminance) and the like.

According to this embodiment, it is possible to perform control whilethe range in which D range over amounts are detected is made to have acertain width. This allows to obtain an image according to user'spreference. In addition, changing the compression ratio in accordancewith a D range over amount can perform tone control without imagesaturation like excessive brightness/excessive darkness.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-089575 filed Apr. 1, 2009 which is hereby incorporated by referenceherein in its entirety.

1. An image processing apparatus which processes and outputs an imagesignal input for each frame, comprising: a division unit which dividesone frame into a plurality of sub-frames; an acquisition unit whichacquires a first image signal constituted by high-frequency componentsand a second image signal constituted by low-frequency components froman image signal of a sub-frame of interest; a unit which generates athird image signal by multiplying the second image signal by a constantvalue K satisfying 0<K<1; a process unit which outputs the third imagesignal when a fourth image signal obtained by adding the first imagesignal and the third image signal falls within a predetermined range andoutputs, when the fourth image signal includes a portion exceeding therange, an image signal obtained by correcting the third image signal soas that the portion does not exceed the range; a unit which generates acomposition signal of the image signal output from said process unit andthe first image signal; a unit which generates a fifth image signal bymultiplying the third image signal by a constant value (2−γ) when γrepresents a correction amount for the third image signal from saidprocess unit; and an output unit which outputs one of the compositionsignal and the fifth image signal as the sub-frame of interest.
 2. Theapparatus according to claim 1, wherein said division unit divides theimage signal of the frame of interest into a plurality of sub-frames byconverting a frame rate of the image signal of the frame of interestinto a frame rate corresponding to a vertical frequency higher than avertical frequency of the image signal of the frame of interest.
 3. Theapparatus according to claim 1, wherein the constant value K is areciprocal of the number of sub-frames constituting the frame ofinterest.
 4. The apparatus according to claim 1, wherein saidacquisition unit acquires the second image signal by using a low-passfilter for the image signal of the frame of interest, and acquires thefirst image signal by subtracting the second image signal from the imagesignal of the frame of interest.
 5. The apparatus according to claim 1,wherein the range is a range of signal levels which a display device asan output destination of said output unit can express.
 6. The apparatusaccording to claim 1, wherein said output unit alternately outputs thecomposition signal and the fifth image signal for each sub-frame.
 7. Theapparatus according to claim 1, wherein said one frame is each of aplurality of partial areas divided from one image.
 8. An imageprocessing method performed by an image processing apparatus whichprocesses and outputs an image signal input for each frame, comprisingthe steps of: dividing one frame into a plurality of sub-frames;acquiring a first image signal constituted by high-frequency componentsand a second image signal constituted by low-frequency components froman image signal of a sub-frame of interest; generating a third imagesignal by multiplying the second image signal by a constant value Ksatisfying 0<K<1; outputting the third image signal when a fourth imagesignal obtained by adding the first image signal and the third imagesignal falls within a predetermined range and outputting, when thefourth image signal includes a portion exceeding the range, an imagesignal obtained by correcting the third image signal so as that theportion does not exceed the range; generating a composition signal ofthe image signal output in the step of processing and the first imagesignal; generating a fifth image signal by multiplying the third imagesignal by a constant value (2−γ) when γ represents a correction amountfor the third image signal in the step of processing; and outputting oneof the composition signal and the fifth image signal as the sub-frame ofinterest.